1. Field of the Invention
The present invention relates to an electrophotograpic recording apparatus based on the electrophotography technique and an electrostatic recording apparatus, and more particularly to a developing apparatus for use in such apparatus.
2. Discussion of the Related Art
In the field of the electrophotograpic recording apparatus, a typically known residual toner cleaning method for removing toner left on the surface of a photoreceptor after the known charging, exposure, developing and transfer steps is a bias cleaning method for removing the residual toner in a manner such that a conductive cleaning member charged by the charge of the polarity opposite to that of the charge of the residual toner is passed over the residual toner carrying surface of the photoreceptor. In the bias cleaning method, the residual toner is removed from the photoreceptor surface by an electrostatic force. Accordingly, the cleaning function depends largely on a charge state of the residual toner. Toner of the opposite polarities and non-charged toner are contained in the residual toner on the photoreceptor surface.
Japanese Patent Unexamined Publication No. Sho. 63-15278 discloses an improved residual toner cleaning technique which uniformly charges the residual toner on the photoreceptor surface by a DC charging unit immediately before a conductive cleaning brush is passed over the photoreceptor, thereby providing an improved cleaning effect. Japanese Patent Examined Publication No. Sho. 55-33075 discloses another technique for providing an easy separation of the residual toner from a light source lamp by weakening the attaching force of the residual toner to the photoreceptor. This technique uses a charge-removal charger and a light source lamp. The light source lamp projects light on a surface area including a discharge area by the charge-removal charger and an area outside the discharge area, simultaneously with the discharging by the charger.
The technique using a charge supply unit, such as a DC charger for improving the function of cleaning the surface of the photoreceptor is known. Where the residual toner is charged by the charging unit, if the quantity of charge is excessive, the attaching force of the residual toner to the surface of the photoreceptor becomes strong. This deteriorates the cleaning function. Further, the voltage of the photoreceptor after the cleaning operation is nonuniform. This nonuniform voltage becomes problematic in the subsequent charging operation.
A tendency of the influence of the current that is fed to the photoreceptor by the charge supply unit (this current is referred to as "fed-in current" hereinafter) upon the cleaning function depends on a charged state of the residual toner. The residual toner may be categorized into the following four types according to the process of forming the residual toner.
1) A toner image was normally transferred to the photoreceptor, but part of the toner layer forming the toner image remains attached to the surface of the photoreceptor (This residual toner is referred to as "normal residual toner".).
2) Another type of toner is the toner having attached to the surface of the photoreceptor in the form of fog, and referred to as "fog residual toner". This toner is different from the toner of the toner image.
3) Still another type of residual toner is such a toner that fails to touch a recording paper owing to jam trouble or a cut-off of a recording paper, and directly receives charge from the transfer unit. This type of toner is referred to as "jam residual toner".
4). Because of improper power supply to the transfer unit, toner is not transferred to the paper, and left on the photoreceptor (This type of toner is referred to as "power supply failure residual toner".).
Thus, the residual toner having different characteristics are present on the surface of the photoreceptor. Therefore, a value of the fed-in current must be kept within a proper range.
In the bias cleaning method, the friction width of the conductive cleaning member and the photoreceptor influences the cleaning function to remove the residual toner from the surface of the photoreceptor and the lifetime of the photoreceptor. If the friction width is outside the proper range, the cleaning efficiency is reduced and the lifetime of the photoreceptor is reduced owing to the abrasion of the photoreceptor.
Further, in the bias cleaning method, the resistance value of the conductive cleaning member influences the cleaning function. The resistance that conductive cleaning member exhibits when the conductive cleaning member stands still with respect to the photoreceptor or the collecting roller, is different from that when it is moving with respect to the same. A matter of significance for the cleaning function is the resistance of the conductive cleaning member when it is moving. The cleaning efficiency for residual toner removal varies depending on this dynamic resistance. The resistance of the conductive cleaning member is also sensitive to a value of the voltage applied to the conductive cleaning member and a state of the contact of the conductive cleaning member with the collecting roller. Therefore, to keep a high cleaning efficiency, it is important to know a resistance of the conductive cleaning member measured under the same condition as in the process of cleaning the photoreceptor. In the electrophotograpic recording apparatus, however, the measurement of the resistance of the conductive cleaning member is usually carried out when it is manufactured or when the cleaning operation is not carried out. Thus, a proper value of the conductive cleaning member during the process of cleaning has not been obtained.
By the way, it is a common practice that the toner collected by the cleaner is thrown away as waste matter or returned as it is to the developing unit.
In recycling the collected toner, paper pieces, fibers of paper, paper particles, dust and other foreign materials that are contained in the toner are problematic.
A technique to remove foreign materials mixed into the toner is disclosed in Japanese Patent Unexamined Publication No. Hei. 3-9384. In the disclosed technique, a net plate is used for a foreign material removing unit. The mesh size of the net is set to be smaller than the gap between the doctor blade and the magnet roll. Foreign materials larger than the mesh size are paper pieces. Therefore, the technique is constructed not taking account of the foreign materials smaller than the mesh size.
The conventional toner recycle mechanism cannot remove minute foreign materials mixed into toner, such as fibers and paper particles. Accordingly, the toner containing minute foreign materials thereinto is used for development. The result is deterioration of print quality owing to reduction of charge quantity in the developer, clogging in the developing unit or defective image caused by foreign materials cohering together, reduction of fluidity of developer, and the like.
An attempt for further reducing the mesh size to catch minute foreign materials creates another problem. A net having such a small mesh size as to block minute foreign materials also blocks the toner.